Apparatus for providing an aerodynamic window

ABSTRACT

An apparatus for maintaining a pressure differential across an aperture between two volumes of different pressure having a circular impeller within a chamber of a circular housing with the outer circular wall of the housing being spaced a predetermined distance from the periphery of the impeller. The circular chamber is positioned between two volumes at different pressures. A flow splitter is positioned adjacent the periphery of the impeller near the aerodynamic window. A first set of vanes near the aerodynamic window directs the gas flow toward the high pressure volume. The differential pressure between the volumes turns the gas flow back in the direction of the low pressure volume. A second set of vanes directs the gas flow into the circular annulus around the impeller.

United States Patent Wilkinson May 27, 1975 APPARATUS FOR PROVIDlNG AN Primary ExaminerC. J. Husar AERODYNAMIC WINDOW Assistant Examiner-Louis J. Casaregola [75] Inventor: David B Wilkinson Xenia Ohio Attorney, Agent, or Firm-Richard T. Killoren [73] Assignee: The United States of America as represented by the Secretary of the [57] ABSTRACT Air Force, Washington. DC. An apparatus for maintaining a pressure differential [22] Filed, May 9 1974 across an aperture between two volumes of different pressure having a circular impeller within a chamber 1 pp 468,329 of a circular housing with the outer circular wall of the housing being spaced a predetermined distance from U S 4l5/53 417/65 the periphery of the impeller. The circular chamber is h 1/00, z #20 positioned between two volumes at different presg Fie'ld 415/53 T sures. A flow splitter is positioned adjacent the periph- '"g 1 cry of the impeller near the aerodynamic window. A i 3 6 1 6 first set of vanes near the aerodynamic window directs the gas flow toward the high pressure volume. The dif- {561 References Cited ferential pressure between the volumes turns the gas flow back in the direction of the low pressure volume.

UNITED STATES PATENTS A second set of vanes directs the gas flow into the cir- Stcigenwald v ular annulus around the impeller 1348,7661 lO/l967 Mugele 417/68 5 Claims, 6 Drawing Figures APPARATUS FOR PROVIDING AN AERODYNAMIC WINDOW BACKGROUND OF THE INVENTION This invention relates to apparatus for maintaining a pressure difference across an aperture through which high intensity radiation is transmitted. Solid windows have been used for supporting pressure differences between the ambient atmosphere and laser cavities. At high energy fluxes, the heating caused by absorption of laser energy may distort the window. Other means have been used in the past for supporting pressure differences between low pressure chambers and the atmosphere, when it is necessary to pass radiation from the chamber to the atmosphere. The patent to Steigerwald, Pat. No. 2,824,232, relates to one such system. This system which relates to periodically providing a path between the chamber and the atmosphere could be used with some types of pulsed lasers but could not be used with all lasers such as the continuous wave laser. AIAA Paper No. 72710 Supersonic Flow Aerodynamic Windows for High Power Lasers given at the AIAA th Fluid and Plasma Dynamics Conference, June 26-28, 1972, discusses some of the problems with high power lasers. This paper discloses the use of a supersonic flow gas stream in an opening between a laser and the atmosphere to form a window for the laser beam. In these systems, the gas is lost after it passes the window. Also, this system is inefficient since the kinetic energy in the gas stream is lost after one pass through the window. To conserve energy and gas in these systems, the gas mass flow is minimized.

BRIEF SUMMARY OF THE INVENTION According to this invention, an aerodynamic window apparatus is provided wherein a larger mass flow can be used since the gas and the kinetic energy, in the gas, is conserved. Since larger mass flows can be used, supersonic flow is not needed and subsonic flow is provided in the aerodynamic window. A double walled housing with a circular outer wall is provided between a high pressure volume and a low pressure volume. A peripheral impeller is provided within the housing to cause a flow of gas around the impeller within the housing. The use of a peripheral impeller permits the introduction of the input gas to the impeller at high speeds, thus making the use of a diffuser unnecessary. A first set of turning vanes gives the gas flow a component toward the high pressure volume. The pressure difference between the volumes then turns the flow back toward the low pressure volume. A second set of turning vanes then turns the flow into the circular annulus around the impeller.

IN THE DRAWING FIG. 1 is a partially schematic side view of an apparatus for providing an aerodynamic window according to the invention.

FIG. 2 is a sectional view of the device of FIG. 1 along the line 2-2.

FIG. 3 is a sectional view of the device of FIG. 1, along the line 3-3 of FIG. 2.

FIG. 4 is a sectional view of the device of FIG. 1 along the line 44 of FIG. 2.

FIG. 5 is a partially schematic isometric view of impeller element and vane element of the device of FIG. 1.

FIG. 6 shows a plurality of aerodynamic window devices according to another embodiment of the invention. I

Reference is now made to FIG. 1 of the drawing which shows an aerodynamic window apparatus 10 secured to a chamber 12, such as a laser cavity, by means of a sealed tubular member 14. The tubular member 14 ,is in line with an aperture 15 in the wall of the housing 16 which is opposite the opening 18. A laser beam or other radiation from chamber 12 is adapted to pass to the atmosphere through the aperture 15 in one wall of housing 16 and then through the aperture 18. A peripheral impeller 20 is positioned within a circular chamber in housing 16 as shown in FIGS. 2 and 3. The peripheral impeller is driven by a motor 21 through a V-belt 22. The outer wall 24 of the chamber is spaced from the tips of the impeller blades 26. A flow splitter 27 is positioned adjacent the periphery of the impeller 20 near the aperture 15.

A plurality of vane members 29, as shown in FIG. 4, are secured to the beam splitter on one side of the aperture 15 to direct the flow toward the aperture 18. A second set of vanes 31 are positioned on the opposite side of aperture 15 from" vanes 29, to direct the flow into the space in the housing 16 between the periphery of impeller 20 and wall 24. In some applications, pressure in chamber 12 could be above the ambient pressure. In this case, the vanes members 29 would be made to direct the flow toward aperture 15.

In the operation of the apparatus, the motor 21 drives the impeller within the housing 16. The exact speed of the motor and impeller would be determined by the ratio of the pulleys and the diameter of the rotor and the desired peripheral speed. This then causes a flow of gas in the space between the impeller and wall 24. The gas flow will be turned by vanes 29 toward the aperture 18, assuming P to be greater than P In the space between vanes 29 and 31, the gas will be turned back toward chamber 12 by the pressure difference P P The flow is then turned into the space between the impeller 20 and wall 24 in housing 16 by vanes 31. Thus, the kinetic energy in the gas is saved and the impeller need only supply the loses.

In an apparatus with a rotor, having a peripheral speed of 800 ft/sec and a three inch column of gas between apertures 15 and 18, and with the dimensions of the apertures approximately equal to the distance between the apertures, wherein the gas flow is turned toward aperture 18 with a radius of curvature of approximately 3 inches, the device will support a pressure ratio P2P1=2.

For large pressure differences, the dimension of the flow between aperture 15 and aperture 18 must be increased. The larger this dimension in a single housing, the greater the chance there will be for secondary flow to develope within the housing, which increases the losses. To avoid this, a plurality of housings may be positioned side by side as shown in FIG. 6. In the device of FIG. 6, three impellers are positioned in a housing 36 with walls 38 between the impellers. Three sets of flow splitters and vanes 39 and 41 are provided. All of the impellers may be driven by a common shaft 43.

There is thus provided an apparatus for providing an improved aerodynamic window which is more efficient than prior art systems.

I claim:

1. An apparatus for maintaining a pressure difference across an opening between a high pressure region and a low pressure region, comprising: a housing having two spaced flat walls and a circular wall interconnecting said flat walls; a first aperture in one of said flat walls adjacent said circular wall; a second aperture in the other flat wall in alignment with said first aperture; means for connecting one of said pressure regions to said first aperture; means for providing a flow of gas along a path within said housing, adjacent said circular wall and past said apertures; means, in the gas flow path on one side of said apertures for directing the gas flow toward the aperture adjacent the high pressure region; and means, in the gas flow path on the other side of said apertures, for redirecting the gas flow into the gas flow path adjacent the circular wall within said housing.

2. The device as recited in claim 1 wherein said first aperture is connected to said low pressure region and said gas flow is directed toward said second aperture.

3. The device as recited in claim 2 wherein said means for providing a flow of gas along a path adjacent said circular wall includes a peripheral gas impeller within the housing with the periphery of said impeller being spaced from said circular wall.

4. The device as recited in claim 3 wherein said means for directing the gas flow toward said second aperture includes a plurality of vanes positioned on one side of said apertures and said means for redirecting the gas flow into the gas flow path within said housing includes a plurality of vanes positioned on the other side of said apertures.

5. The device as recited in claim 4 wherein a flow splitter is positioned near the periphery of said impeller adjacent said apertures; said vane members being secured to said flow splitter.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,885,884

DATED I May 27, 1975 INVENTOR(S) David B. Wilkinson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 51, change "P P =2" to P /P =2 an.

Signed and Sealed this second Day Of September 1975 [SEAL] A rresr:

RUTH C. MASON C. MARSHALL DANN Arresting ()ffr'ver (mnmr'ssimur uflalenrs and Trmlemurkx 

1. An apparatus for maintaining a pressure difference across an opening between a high prEssure region and a low pressure region, comprising: a housing having two spaced flat walls and a circular wall interconnecting said flat walls; a first aperture in one of said flat walls adjacent said circular wall; a second aperture in the other flat wall in alignment with said first aperture; means for connecting one of said pressure regions to said first aperture; means for providing a flow of gas along a path within said housing, adjacent said circular wall and past said apertures; means, in the gas flow path on one side of said apertures for directing the gas flow toward the aperture adjacent the high pressure region; and means, in the gas flow path on the other side of said apertures, for redirecting the gas flow into the gas flow path adjacent the circular wall within said housing.
 2. The device as recited in claim 1 wherein said first aperture is connected to said low pressure region and said gas flow is directed toward said second aperture.
 3. The device as recited in claim 2 wherein said means for providing a flow of gas along a path adjacent said circular wall includes a peripheral gas impeller within the housing with the periphery of said impeller being spaced from said circular wall.
 4. The device as recited in claim 3 wherein said means for directing the gas flow toward said second aperture includes a plurality of vanes positioned on one side of said apertures and said means for redirecting the gas flow into the gas flow path within said housing includes a plurality of vanes positioned on the other side of said apertures.
 5. The device as recited in claim 4 wherein a flow splitter is positioned near the periphery of said impeller adjacent said apertures; said vane members being secured to said flow splitter. 